1. Field of the Invention
The present invention relates to an organic electrophotographic photoconductor in the type of having functionally distinguished laminate layers.
2. Description of the Related Art
As disclosed in Japanese Patent Application Publications No. 42380/1987 and 34099/1985, in recent years, organic electrophotographic photoconductors of the type having functionally distinguished organic laminate layers, a charge-generation layer and a charge-transport layer which are applied on an electroconductive substrate in that order, have been developed and provided in practical uses. In general the electrophotographic photoconductor is formed by the process including steps of: preparing a solution by dissolving and dispersing an organic charge-generation material and a resin binder in an organic solvent; applying the solution on a surface of an electroconductive substrate made of an aluminum alloy and drying the solution to provide a charge-generation layer; preparing another solution by dissolving and dispersing an organic charge-transport material and a resin binder in an organic solvent; applying the solution on a surface of the charge-generation layer and drying the solution to provide a charge-transport layer. Additionally, the charge-transport layer may include an additive such as an antioxidant.
In spite of the structure described above, the conventional organic electrophotographic photoconductor may readily cause some troubles, for example image deterioration such as a light gray appearance in non-image areas and a blank unprinted appearance in image areas in a copy formed by a copying machine of a positive development type. In addition, printing defections such as black dots in non-image areas and lowering of printing concentration under a repetitive printing process may be also observed in a copy formed by an electrophotocopying machine of a negative development type, such as a laser printer.
It is considered that these troubles are caused by variations in the physical and chemical properties and also variations in rough surfaces of the charge-generation layer and the charge-transport layer which are formed on a defective surface of the electroconductive substrate. To improve these troubles, there is an idea of providing a resin layer and an intermediate layer or sub-layer between the electroconductive substrate and the charge-generation layer. Furthermore, it has been known that an alcohol-soluble polyamide resin can be provided as a preferable material for the layer (see Japanese Patent Application Publication No. 45707/1983 and Japanese Patent Application Laying-open No. 168157/1985).
In the steps of manufacturing the conventional electrophotographic photoconductor described above, a surface of the electroconductive substrate is shaved with a diamond tool or the like and then the shaved surface is ground to a predetermined surface roughness by means of grinding or the like. After the grinding step, machine oil, grinding oil, and other unnecessary materials are removed from the surface of the substrate by treating with a cleaning agent. Then the intermediate layer, the charge-generation layer, and the charge-transport layer are applied on the substrate in that order. Conventionally, an appropriate organic base solvent such as trichloroethylene and Freon.RTM. has been used as the above cleaning agent. However, the organic base solvents are now regarded as industrial pollutants that deplete the ozone layer. In recent years, therefore, the use of water-soluble weak- alkali detergents has been recommended for avoiding the environmental disruption. In this case, however, there is a problem of forming etch-pits on the surface of the substrate during the step of washing the substrate with the weak alkali detergent.
The electroconductive substrate of aluminum alloy can be easily etched by the water-soluble detergent such as the weak alkali. In this connection, furthermore, the aluminum alloy comprises an area to be easily etched by the detergent. That is, the aluminum alloy usually comprises an element such as iron that has a higher oxidation-reduction potential compared with that of aluminum, so that for example an iron-rich portion and its surroundings formed in the aluminum alloy can be more easily etched than the other portions. In this case, an etched-pit with a diameter of in the order of 1.times.10.sup.-1 to 3.times.10.sup.-1 can be sometimes formed in the electroconductive substrate.
Consequently a surface level of the substrate becomes uneven after being subjected in the washing step. For this reason, furthermore, a part of the intermediate layer to be applied thereon also becomes thicker while another part thereof becomes thinner. In the uneven intermediate layer, a local leak of electrons can be observed in its relatively thin portion, resulting in an defective image with a whiteness, an unexpected black dot, or the like. This kind of phenomena may be not observed at the beginning but it will be actualized with the accumulation of electrons after repeating image formations (for example forming images on 10,000 sheets of A-4 sized paper). In the case of the relatively thick portion of the intermediate layer, a residual potential is increased by the accumulated electrons and thus the image to be formed can be polluted or degraded.